A wide variety of soap bar compositions and manufacturing processes are known in the art. Commonly, soap bar compositions for toiletry purposes are milled soaps of low moisture content (from about 5% to about 18% water) based on a mixture of tallow and coconut oil feedstocks. Bars having milled soap characteristics can also be prepared from soap of a high moisture content, as described for example in U.S. Pat. No. 2,686,761 and U.S. Pat. No. 2,970,116 by mechanically working the soap at a temperature of from about 80.degree. F. to 125.degree. F. and by using an appropriate fat feedstock. Such a process has two main advantages; firstly, it is relatively energy-efficient in that less drying of the neat-kettle soap is required; and secondly, it produces soap bars having desirable translucency or transparency as a result of beta-phase soap formation.
From the consumer acceptance viewpoint, of course, the lathering characteristics of a toilet bar composition are highly important and there is a continuing need to improve this area of performance. Traditionally, lather enhancement has been achieved in two ways. Firstly, shorter chain fatty acid soaps such as coconut soaps are known to produce a much richer lather than longer chain fatty acid soaps such as those based on tallow and it is therefore common practice in toilet bar manufacture to add up to 50% coconut soap to the tallow fat feedstock. Secondly, superfatting agents such as coconut fatty acid also improve the volume and richness of the lather when added to toilet bars in levels of up to about 10%. At higher levels, however, coconut soaps increasingly have a detrimental effect on bar mildness while fatty acids can produce undesirable softening of the bar. Moreover, coconut soaps and fatty acids are both expensive commodities and it would therefore be desirable to achieve improvements in lathering without recourse to high levels of these ingredients.
In the case of beta-phase soaps, moreover, there is a more fundamental difficulty in achieving high lathering. Fat feedstocks which are relatively rich in shorter chain (less than 16 carbon atoms) saturated fatty acids inhibit the formation of beta-phase soap and are therefore unsuitable for making transparent or translucent soap bars. In a similar way, beta-phase soap formation is also inhibited by the addition of free fatty acid superfatting agents in levels above about 1%-2%. For all these reasons, therefore, it has not been possible hitherto to achieve significant improvements in the lathering characteristics of beta-phase soaps.
Another drawback of beta-phase soaps is that they are relatively soft and display much poorer smear characteristics than traditional omega-phase soaps. Accordingly it would be highly desirable to improve the smear characteristics of beta-phase soap compositions.
It has now been discovered that the addition of defined low levels of certain water-insoluble silicas or silicates has a beneficial effect on bar lathering characteristics, both in soft and hard water conditions; that the lather benefits result even in the case of superfatted toilet bars based on a high coconut oil feedstock; that unexpectedly, the lathering improvement is achieved without detriment to beta-phase soap formation and without loss of transparency or translucency; that the smear characteristics of beta-phase soap bars is also markedly improved by use of the additives; that in addition, cleansing performance is improved; and, unexpectedly, that the skin-feel characteristics of the bar are also significantly modified.
The in-situ formation of water-insoluble silicas in detergent bars has previously been described in Soap/Cosmetics/Chemical Specialities, June 1976, pp. 43 to 66. Silica levels of 9% or more were examined and lathering improvements in hard water were reported. By contrast, in the present invention lather benefits are observed both in hard and soft water but only in defined low additive levels, the benefit diminishing or disappearing outside the specified range.